Low Saxon War

The Low Saxon War occurred from 1625 to 1630 when Denmark-Norway, led by King Christian IV of Denmark, intervened in the greater Thirty Years' War. The Danish intervention resulted in the 1626 Battle of Lutter, in which their army was crushed.

Background
The termination of the Palatinate campaign in 1623 ended the Protestant Electoral Palatinate's war with the Holy Roman Empire, and it seemingly brought the Thirty Years' War to an end. However, the balance of power had been so disrupted that King Christian IV of Denmark sought to exploit the Holy Roman Empire's weakness to pursue expansionist dynastic aspirations in northern Germany, as the ruling House of Oldenburg also ruled over the German principality of Oldenburg. Fearing that the Austrian Habsburgs would trample German liberties and increase their authority, and seeking to seize Bremen, Verden, and Osnabruck to acquire the Elbe and Weser River trade routes, the Danes allied with England and Scotland and prepared for war. In January 1625, despite lacking the support of his privy council, Christian IV raised his own army in order to war with the Empire.

War
In early 1626, Christian concentrated his 20,000-strong army at Wolfenbuttel in order to keep the Imperial armies of Albrecht von Wallenstein and Count Tilly divided. Wallenstein occupied Magdeburg and Halberstadt to feed and fund themselves at the expense of the local population, and he began operations around Goslar before receiving reports that Ernst von Mansfeld was advancing south along the Elbe to liberate Magdeburg. Mansfeld attempted to cut off the Imperial supply route at Dessau, but Wallenstein counterattacked and defeated Mansfeld in the Battle of Dessau Bridge. Mansfeld rushed east and then south from Silesia to upper Hungary to rendezvous with the Transylvania ruler Gabriel Bethlen, and, while Wallenstein initially halted his army to respect Brandenburg's neutrality, he later set out with 20,000 troops to catch up with Mansfeld's troops. Meanwhile, Tilly captured and razed the strongholds of Munden, Northeim, and Gottingen, massacring and plundering throughout the campaign. Christian IV marched south to attempt a relief, but he was too late. He then retreated north to reach Wolfenbuttel, but he was harried by enemy forces along the way. On 27 August 1626, Tilly's army caught up with him at Lutter am Barenberge, and the ensuing Battle of Lutter saw the Danish army be forced to abandon its artillery and retreat, suffering a major defeat. To the southeast, the Ottoman-supported Hungarians under Bethlen were forced to make peace, while Mansfeld died of disease in the Balkans while trying to evade Wallenstein. Tilly then besieged Nienburg and Wolfenbuttel, and Wallenstein joined Tilly north of Luneberg in September 1626 and overran Holstein, forcing the Danes to retreat. Wallenstein was then made Duke of Mecklenburg as a reward, and, seeking to gain a base for a fleet, he had Stralsund besieged. From May to August 1628, the city of Stralsund held out against Wallenstein's army, and Sweden entered the war in order to support the Hanseatic League city against the besiegers; the battle was noteworthy for the bravery of the Scots fighting for the Protestant side. On 4 August, Wallenstein ordered his army to retreat, suffering his first defeat. King Christian IV then assembled his army on the island of Usedom and took Wolgast without any resistance from the Imperial garrison. Christian turned Wolgast into a fortress and waited for Wallenstein for the final battle. The ensuing Battle of Wolgast was a decisive Imperial victory, and Christian's badly battered army was forced to withdraw to Denmark, leaving the Catholic cause ascendant once again. The 1629 Treaty of Lubeck ended the war between Denmark and the Holy Roman Empire, but the Edict of Restitution caused the moderate Lutherans of Saxony and Sweden to continue the Protestant struggle.